1. Field of the Invention
The present invention relates to a lubrication structure for an engine, such as a four-cycle engine.
2. Description of the Relevant Art
A lubrication system for an engine, such as a four-cycle engine, is disclosed in the background art. For example, Japanese Patent Publication No. Hei. 6-25527 discloses a lubrication system. In the background art, a crank web is provided in the crankcase. A distance between a lower inner surface of the crankcase and an outer periphery of the crank web is set almost uniformly around the peripheral direction of the crank case. This structuring of the background art makes it relatively difficult to discharge oil from an oil discharge port.
It is an object of the present invention to solve one or more of the drawbacks associated with the background art.
It is a further object of the present invention to provide a lubrication system with improved oil discharge performance from a crank chamber.
These and other objects are fulfilled by an engine comprising: a crankcase; a crank chamber formed inside said crankcase; a crankshaft housed inside said crank chamber, said crankshaft rotating in a rotation direction; a crank web attached to said crankshaft; an oil discharge port formed in a lower section of said crank chamber; a first distance formed between an outer periphery of said crank web and a first inner surface of said crankcase, said first inner surface being downstream of said oil discharge port in said rotation direction; and a second distance formed between said outer periphery of said crank web and a second inner surface of said crankcase, said second inner surface being upstream of said oil discharge port in said rotation direction, wherein said first distance is less than said second distance.
Moreover, these and other objects are fulfilled by an engine comprising: a crankcase; a crank chamber formed inside said crankcase; a crankshaft housed inside said crank chamber, said crankshaft rotating in a rotation direction; a crank web attached to said crankshaft; an oil discharge port formed in a lower section of said crank chamber, said oil discharge port being defined in part by a back edge, wherein said back edge is wedge shaped and points in a direction opposite said rotation direction, at least at a section corresponding to said crank web.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.